The invention relates to a device and a process for liquid treatment of a defined area of the main surface of a wafer-shaped article, especially a wafer.
The reason for treatment of a defined section of a wafer-shaped article, i.e. the section near the edge, especially of a wafer, will be described below.
A wafer, for example a silicon wafer, can have for example a coating of silicon dioxide on all sides. For subsequent processes (when for example a gold layer or a layer of polysilicon (polycrystalline silicon) is to be applied) it can be necessary to remove the existing coating from the wafer at least in the edge area of the main surface, but also optionally in the area of its peripheral surface and/or the second main surface. This takes place by etching processes which can be divided mainly into dry etching processes and wet etching processes. It can also be desirable to remove a metal (for example, copper) which was applied galvanically beforehand from certain areas of the main surface of the semiconductor substrate. In this case, this area can be either an annular section near the edge, or exactly the area of the front main surface (main surface on which the structures are located=device side), in which there are no structures, i.e. the chip-free zone.
Another application is the cleaning of wafers. Here it can be necessary to clean the wafer at least in the edge area of the main surface, but optionally also in the area of its peripheral surface and/or the second main surface, i.e. to remove particles and/or other contamination. This is done by wet cleaning processes.
Another liquid treatment is the application of layers, for example galvanic application of metals (electroplating). This can be done with or without current, in the latter case its being “Electroless Electroplating”.
The invention is aimed at wet etching, wet cleaning or wet chemical application of layers (combined under the concept of liquid treatment). The surface section of the wafer to be treated is wetted with the treatment liquid and the layer to be removed or the impurities are removed or a layer is built up in this surface section.
During liquid treatment the wafer-shaped article can be either stationary or can rotate (for example, around an axis).
To prevent the treatment liquid from reaching the surface not to be treated in an uncontrolled manner, EP 0 316 296 B1 suggests a carrier (chuck) which flushes the surface, which faces the carrier and which is not to be treated, with a gas. In doing so the gas emerges between the edge of the wafer and the carrier.
JP 09-181026 A describes a carrier for semiconductor wafers which outside an annular nozzle has a special shape, for example an annular step which falls off to the outside, or a bevel of its edge. An intake opening is also proposed. The flow velocity in the edge area will be influenced (reduced) by this shaping or by the intake opening. This is intended to be used to allow the treatment liquid applied from the top to flow beyond the edge of the wafer onto the side facing the chuck and to treat an edge area there.
Regardless of whether a means for accommodating the wafer-shaped article (carrier or chuck) as claimed in EP 0 316 296 B1 or JP 09-181026 A (English abstract) is used, on the main surface facing the carrier an edge area of 1.5 mm (measured from the outer edge of the wafer) at maximum is treated. Afterwards, the liquid flows back in the direction of the wafer edge and is flung off by it. This treated edge area is not intentionally defined in either of the two cases, rather it is a random result, since the size of the edge area depends largely on a plurality of parameters which mutually influence one another to some extent, such as the surface composition (roughness, type and thickness of the adsorption layers), temperature, pressure, humidity, etc.
U.S. Pat. No. 4,838,289 A discloses a system for etching the edge of a wafer, in which a nozzle is pointed against the area of the wafer surface to be treated while the wafer rotates. The defect of this system is that the area to be treated is not exactly defined and also liquid can reach the area which is not to be treated.